The effect of nitrogen application on the competitiveness of corn at different densities of Johnson grass (Sorghum halapense)

In order to investigate the effect of nitrogen application on corn competitive ability with Johnson grass (Sorghum halapense) at different densities, An experiment was conducted as factorial arrangement based on completely randomized block design with three replications at researcher greenhouse of Islamic Azad university, Sabzevar Branch in 2015. Factors were: Nitrogen Levels (recommended (90 Kg.ha-1 of N) and recommended%(135 Kg.ha-1 of N)) and Johnson grass density (0, 1, 2 and 3 plants. Pot-1(0, 15, 30 and 45 plants. m-2, Respectively). Corn and Johnson grass were planted in pot with 30 cm diameter containing approximately 10 kg soil. Corn density was five plants per pot. Analysis variance result showed that chlorophyll index, stem dry weight, root diameter, root volume, root dry matter and root/shoot ratio affected by nitrogen levels. Increasing nitrogen amount increased these characteristics. Increasing Johnson grass density decreased chlorophyll index (7.89%), stem dry weight (16.48%), root diameter (21.31%), root area (22.18%), root volume(22.99%) and plant height (1.1%). Other corn root trait was not affected by Johnson grass density. Overall. Nitrogen application increased competition ability of corn with johnson grass, whereas increasing of Johnson grass density had negative impact on corn root morphological.